4890, 4850x2, 4870x2, but the last two suck power like you wouldn't believe. You'll be giving up lower idle power draw and DX11 if you went down to the 4XXX series, stick with what you have and look at the 58XX series.

Here's a Palit GTX 560 for $249.Edited by jellis142 - 4/3/11 at 2:29pm